Caulastrea (Caulastrea furcata)
Caulastrea furcata is classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix II of CITES (2).
A low-growing coral of tropical reefs in the Indo-West Pacific, Caulastrea furcata has fleshy polyps with thick septa that give a prominent radiating stripe pattern to the upper surface (3).
As in other colony-forming corals, colonies of Caulastrea furcata are composed of numerous small polyps, soft-bodied animals related to anemones. Each polyp bears numerous tentacles that direct food into a central mouth, where it is digested in a sac-like body cavity. One of the most remarkable and ecologically important features of these corals is that the polyps secrete a hard skeleton, called a ‘corallite’, which over successive generations contributes to the formation of a coral reef. The coral skeleton forms the bulk of the colony, with the living polyp tissue comprising only a thin veneer (3).
The corallites of Caulastrea furcata are elongate, usually oval, and rather shallow. The corallite branches diverge at varying angles and divide at different lengths from the base (3) (4). Living colonies of Caulastrea furcata are usually brown or green, with green oral discs (3).
Caulastrea furcata is found in the Indo-West Pacific, ranging from the southwest and northern Indian Ocean, through Southeast Asia, to Japan, the East China Sea, eastern Australia and the West Pacific (1).
Occurring on tropical, protected, shallow reef slopes where the substrate is partly sandy, Caulastrea furcata forms extensive stands that may measure over 5 metres across. It has been recorded to depths of at least 30 metres, and may also be found in lagoons (1) (3) (4).
Like many coral species, Caulastrea furcata is zooxanthellate, which means that its tissues contain large numbers of single-celled algae called zooxanthellae. The coral and the algae have a symbiotic relationship in which the algae gain a safe, stable environment within the coral’s tissues, while the coral receives nutrients produced by the algae through photosynthesis. By harnessing the sun’s energy in this way, corals are able to grow rapidly and form vast reef structures, but are constrained to live near the water’s surface. While, on average, a zooxanthellate coral can obtain around 70 percent of its nutrient requirements from the photosynthesis of the zooxanthellae, the coral may also feed on zooplankton (3).
Very little is known about the specific reproductive biology of Caulastrea furcata, although it is likely to be able to reproduce both sexually and asexually. Asexual reproduction occurs via fragmentation, in which a branch breaks off a colony, reattaches to the substrate and grows. Sexual reproduction occurs via the release of eggs and sperm into the water. Some of the resulting larvae from these spawning events settle quickly on the same reef, whilst others may drift around for months, finally settling on reefs that may be hundreds of kilometres away (3).
With an estimated 20 percent of the world’s coral reefs already destroyed, Caulastrea furcata faces many of the threats that are affecting coral reefs globally (5) (6). Worldwide, there is increasing pressure on coastal resources resulting from human population growth and development. There has been a significant increase in domestic and agricultural waste in the oceans, poor land-use practices that result in an increase in sediment running onto the reefs, and over-fishing, which can have ‘knock-on’ effects on the reef (5).
However, the major threat to corals is global climate change, with the expected rise in ocean temperatures increasing the risk of coral ‘bleaching’, in which the stressed coral expels its zooxanthellae, often resulting in the death of the coral (6). Climate change may also lead to more frequent, severe storms, which can damage reefs, and rising carbon dioxide levels may make the ocean increasingly acidic. Such stresses can also make corals more susceptible to disease, parasites and predators, such as the crown-of-thorns starfish (Acanthaster planci) (5) (6) (7).
In addition to being listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), which makes it an offence to trade this species without a permit, Caulastrea furcata also forms part of the reef community in numerous Marine Protected Areas (1) (2). To specifically conserve this coral, recommendations have been made for a raft of studies into aspects of its biology, population status, habitat and the threats to its survival (1).
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- Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
- Asexual reproduction: reproduction that does not involve the formation of sex cells (‘gametes’). In many species, asexual reproduction can occur by fission (or in plants ‘vegetative reproduction’); part of the organism breaks away and develops into a separate individual. Some animals, including vertebrates, can develop from unfertilised eggs; this process, known as parthenogenesis, gives rise to offspring that are genetically identical to the parent.
- Colonies: a group of organisms living together. Individuals in the group are not physiologically connected and may not be related, such as a colony of birds. Another meaning refers to organisms, such as bryozoans, which are composed of numerous genetically identical modules (also referred to as zooids or ‘individuals’), which are produced by budding and remain physiologically connected.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Photosynthesis: metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.
- Polyp: typically sedentary soft-bodied component of cnidaria, a group of simple aquatic animals including the sea anemones, corals and jellyfish. A polyp comprises a trunk that is fixed at the base, and a mouth that is placed at the opposite end of the trunk and is surrounded by tentacles.
- Septa: in a coral, radial elements that project inwards from the corallite wall (the skeletal wall of an individual coral polyp).
- Spawning: the production or depositing of large quantities of eggs in water.
- Symbiotic relationship: relationship in which two organisms form a close association. The term is now usually used only for associations that benefit both organisms (a mutualism).
- Zooplankton: tiny aquatic animals that drift with currents or swim weakly in water.
IUCN Red List (March, 2011)
CITES (March, 2011)
- Veron, J.E.N. (2000) Corals of the World. Australian Institute of Marine Science, Townville, Australia.
- Dai, C.F. and Horng, S. (2009) Scleractinia Fauna of Taiwan. II. The Robust Group. National Taiwan University Press, Taipei, Taiwan.
- Wilkinson, C. (2004) Status of Coral Reefs of the World: 2004. Volume 3. Australian Institute of Marine Science, Townsville, Australia.
- Carpenter, K.E. et al. (2008) One-third of reef-building corals face elevated extinction risk from climate change and local impacts. Science, 321: 560-563.
- Miththapala, S. (2008) Coral Reefs. Coastal Ecosystems Series (Volume 1). Ecosystems and Livelihoods Group Asia, IUCN, Colombo, Sri Lanka.